Volcano Watch: What makes the lava lake within Halema‘uma‘u rise and fall?

On Jan. 8, Kilauea Volcano’s summit lava lake level was 38 m (125 ft) below the rim of “Overlook crater,” the small crater that formed above the active vent in Halema‘uma‘u. The lava lake continuously emits elevated levels of sulfur dioxide gas and erupts small, but measurable, amounts of Pele’s hair and other ash-sized tephra (airborne lava fragments) that accumulate on the rim of Halema‘uma‘u (lower right) and areas downwind of the lake.

About a year ago, the lava lake within Halema‘uma‘u at Kilauea Volcano’s summit was high enough that spattering on the lake surface was commonly visible from the Jaggar Museum overlook in Hawaii Volcanoes National Park. Although nighttime glow from the lava lake remains impressive, direct views of spattering lava are now less common because the lake level gradually dropped since that time.

The lake level is constantly changing, and it fluctuates throughout many different timescales, from minutes to months. So what causes the lake level to rise and fall?

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To answer this question, USGS Hawaiian Volcano Observatory scientists have been closely observing the lava lake behavior and making careful, regular measurements of the lake level. A key to understanding the processes that control lake level is to compare the lake level measurements to other monitoring parameters, such as gas emission rates, ground tilt, and seismic tremor. Direct visual observations of lake activity also are essential.

With several years of such data, we can show that the lake level is related to two main factors: magma chamber pressure and gas emission rates.

Magma chamber pressure is the main control on the lava lake level. On a day-to-day basis, the lake level rises and falls in concert with the volcano’s deflation-inflation cycles. Deflation results in lava levels dropping as much as 20 meters (yards) throughout several days, with inflation leading to lake level rise.

Throughout longer time periods, such as months to years, magma chamber pressure is affected by the rate of magma supply from deeper levels. For example, an apparent increase in magma supply rate in early 2016 caused the volcano to inflate slightly and drove the lake higher. The decline in the lake level during the past year might relate to a slight decrease in magma supply rate.

The close correlation between magma chamber pressure and lava lake level means the lake can be thought of as a “barometer” for the underlying magma chamber.

The lake provides a tool for judging the pressure state of the volcano, which is potentially useful for anticipating future eruptive events on Kilauea’s rift zones. For example, the lake rose to high levels just before the March 2011 Kamoamoa fissure eruption near Pu‘u ‘O‘o on the volcano’s East Rift Zone.

The pressure of the summit magma chamber also determines the rate at which magma is flowing to Pu‘u ‘O‘o on the East Rift Zone. Higher lake levels in Halema‘uma‘u normally mean elevated lava supply rates at the Pu‘u ‘O‘o vent, and potentially more vigorous lava flows. So tracking the lake level can be another tool for forecasting lava flow hazards on the East Rift Zone.

Gas emission rate is the other main control on the Halema‘uma‘u lava lake level. Increases in the gas emission rate from the lake relate to increases in the amount of spattering on the lake surface. Releasing more gas from the lake results in a slight drop in lake level, normally of a few meters (yards).

Unlike the lava level changes because of magma chamber pressure, these gas-driven changes normally occur throughout much shorter time periods, ranging from minutes to hours.

HVO scientists normally measure the lake level with a hand-held laser range finder, but new tools for tracking lava lake level are on the horizon. University of Cambridge scientists currently are testing a radar system to continuously measure Kilauea’s summit lava lake level with high precision. Stereo cameras also are being tested this month to track the lake level, as well as changes in crater and lake dimensions.

The level of the Halema‘uma‘u lava lake is a simple indicator of the pressure state of Kilauea’s magma chamber, and the lake provides a “window” for peering into the volcano’s interior. The lake has provided another useful tool to add to HVO’s monitoring toolbox.

Speaking of Halema‘uma‘u, you’re invited to attend a Volcano Awareness Month presentation about Kilauea Volcano’s summit eruption. The presentation is slated for Jan. 16 in Hawaii Volcanoes National Park. On Jan. 17, a “talk story” event focused on Mauna Loa will be hosted in the Ocean View Community Center. The Volcano Awareness Month schedule and program details are posted on HVO’s website (https://volcanoes.usgs.gov/hvo/), or you can email askHVO@usgs.gov or call 808-967-8844 for more info.

Volcano activity updates

This past week, Kilauea Volcano’s summit lava lake level fluctuated with summit inflation and deflation, ranging about 30-47 m (98-154 ft) below the vent rim. On the East Rift Zone, the 61g lava flow remained active downslope of Pu‘u ‘O‘o, with scattered breakouts on the pali and coastal plain, but no ocean entry. The 61g flows do not pose an immediate threat to nearby communities.

Mauna Loa is not erupting. Rates of deformation and seismicity remain above long-term background levels, but rates are decreased from earlier in the year. Similar decreases occurred in the past during the ongoing period of unrest; it is uncertain if these lower rates will persist or pick up again in the near future. Small-magnitude earthquakes occurred beneath the summit caldera and upper Southwest Rift Zone at depths less than 5 km (3 mi). A few deeper earthquakes were scattered beneath the volcano’s southeast flank at depths of 5-13 km (3-8 mi). GPS and InSAR measurements continue to show deformation related to inflation of a magma reservoir beneath the summit and upper Southwest Rift Zone. No significant changes in volcanic gas emissions were measured.

No earthquakes were reported felt on the Island of Hawaii this past week.

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